Growers must not let that happen, he stresses. "One plant can cover several square metres, and can return up to 500 seeds to the soil." At least 98% control is needed to prevent numbers increasing in future years, he explains.

"Partial autumn control adds to the headache. If growers become complacent, they are in for a nasty surprise. Late cleavers problems caused by stunted plants which remain unnoticed in the bottom of the crop have increased."

Growers must be "extremely vigilant" to identify such weeds and to ensure they are sprayed with Starane at the best time, Mr Gurney maintains. Control must be delayed, perhaps as late as boots swollen (GS45), until weeds have recovered.

Growing away

"Unless cleavers have started growing away from the autumn treatment, they are not going to be in a fit state to spray, and acceptable control levels will not be achieved."

Several seasons of HGCA-funded ADAS trials and commercial field experience suggest otherwise, argues head of cereals Jim Orson.

Using appropriate rates of DFF in the autumn and following up with Starane in mid to late April shows that at any given dose more reliable weed control is obtained, he says.

"But it is worth waiting for good growing conditions in the spring. Go by this rather than how the weed looks." It is difficult to give firm dose recommendations, he adds. "Rain up to a month after application can influence performance. So beware dropping too low if unsettled weather is likely."

John Burgess, Agrevos cereal herbicides product manager maintains Eagle (amidosulfuron) will also give "excellent" control of DFF-affected cleavers. Being less temperature dependant than Starane, it can be applied earlier, he adds.

"Although you wouldnt want to apply it to dormant cleavers, they only need to be growing slowly to be controlled."

&#8226 Tailor to problem.

&#8226 Aim for 98% control.

&#8226 With Starane, 0.5-1 litre/ha depending on

– weed size

– weed growth

– crop competition

– weather.

&#8226 With Eagle, 20-40g/ha depending on weed size.

A growing problem? A cleavers study carried out by Valerie Prout of Produce Studies for DowElanco shows that the area of cereals sprayed for cleavers has nearly doubled in the past six years. Though changes in cultivation and rotation practice have had an impact, DowElancos David Gurney believes poor timing and excessively low doses resulting in less than 98% control have allowed populations to build up.